[Ricochet]

Durability: we'd like to see a gas system that offers the realism of heavily actuating parts that doesn't beat up on itself ...high grade steel and extremely high grade polymers would be a good start ...maybe carbon fibre?

Air seal and hop-up: the two most important factors in BB trajectory. Allow for a large and extremely aggressive bucking system that easy to work on. Also a perfectly fit together parts and simple system that capitalizes on excellent air seal. Avoid AEG or old hop designs. Check out Systema's for a few ideas.

FPS valve: a no brainer would be an FPS control valve, so one doesn't need to be installed aftermarket.

Robust internal system: look towards the Systema PTW. Everything clicks together "perfectly". Moving bolt, hop-up system, etc.

Magazines: must have a clever seal system, and be reliable. Make them easy to clean, rebuild, etc; and not to wear out easily.

Gas system: make sure the gas system can handle everything from CO2, to green gas, and all heat tolerances and variables and still fire flawlessly.

Upgrade ability: a good gun is easy to disassemble, and doesn't contain any cheap or useless parts. It's nice to be able to quickly do a barrel swap or switch out the bucking.

Cost: cost will reflect the build, but I'd rather pay $1000 or more for a ridiculously good build than buying something where the company tried to save money.

Performance: if your going to bother making it durable, dependable, and reliable, them it must shoot outstanding as well.

Bells abd whistles: RA-Tech has made some good upgrades for existing systems, check out some of their ideas. Look into things like perfectly milled stainless steel inner barrels, etc.